It is not unusual to mount fuel pumps inside a fuel tank for automotive vehicles. The fuel pump is typically part of a fuel dispensing unit which includes a fuel level sensor, a fuel filter and a structural member such as a flange mounted sealably to a fuel tank. During assembly, the fuel pump and level sensor are inserted through an opening in the fuel tank as one assembled unit, and the flange is engaged sealably to an exterior side of the fuel tank. An elastomeric O-ring provides the seal between the flange and the fuel tank. Electrical power typically routes to the internal devices within the fuel tank (pump and sensor) through an electrical fitting mounted to the flange.
Stringent government environmental regulations are persuading the automotive industry to make a closer study of fuel vapor permeation through a fuel tank. In many instances, the once popular, light weight, plastic fuel tank is being replaced with impermeable steel tanks. Aside from the walls of a plastic fuel tank, another source of permeation is through the electrical fitting which penetrates the flange. A multitude of wires electrically connect to the internal devices of the fuel tank; therefore, a corresponding multiple of terminal pins penetrate the flange. Each pin penetration is a potential source for vapor leakage. Existing electrical fittings do not provide a hermetic seal, but use rubberized seals or elastic grommets to minimize permeation. However, temperature variations and aging degrade the integrity of the seals, resulting in a loss of the permeation barrier.